cooling fan

[smoken u]

Hi all, I have been having an issue with the cooling fan not turning on, so i went out today to try and diagnose the problem, with some aid from the bently manual, i tried jumping the thermoswitch for both high and low speed fan control, nothing happened, so i checked for 12v of power at terminal 3 (red wire at thermoswitch connector) again nothing, so i check the red power wire for continuity, it is fine, indicating that it is not broken, so i went and repalce the fan relay, and fuse and cleaned all the connections, tried testing again, and still nothing. now the cylinder head is off the car getting im doing the HG on it, and i am using a 40 amp battery charger as a power source for all my testing. i cant figure this one out, short of putting a 3 way switch directly to the fan motor for turning it on/off and high speed, im stumped

[truckoSaurus08]

Is your ground side hooked up? Im assuming its for your 1990 jetta. The circuit according to a bentley wiring diagram is pretty simple. 1 red power wire to the thermo switch and two red wires with white and black on them going to the motor. each for a different speed. Have you tried jumping the motor directly? Maybe with your head pulled your not grounded?

[smoken u]

ill have to check about that grounding, i never even thought of that, and no i havent tried jumping the motor directly yet, but ill give it a shot

[smoken u]

ok just got back in from more testing, i completely rung the circuit out, checked the whole thing for continuity, even checked the resistor for its correct value, most of it checked out fine, but the 3rd pin on the thermoswitch, (red wire) which is supposed to be energized at all times, isnt, ive got no power to it, checked all the fuses, they all check ok, even replaced the relay. would it be possible as a fix to place a 30 amp fused link on the 3rd pin of the thermoswitch, and have that connected directly to the battery?? or would that cause a paracitic drain on the battery?? which wold suck becasue im gonna need all the starting power i can get come the cold weather.

[truckoSaurus08]

I just looked up the diagram for a 1990 jetta with A/C on a TD and boy is that a cluster #!*%$. Any way if you have A/C then it looks like you will have series resistor in line with the motor. that leg of The circuit is activated when you turn the a/c on full blast. So the fan should run whether or not the thermoswitch is working. Also The cooling fan circuit shares the same ground as the a/c clutch and according to the diagram that ground is located in the headlight wiring harness.
Oh and to answer your question, you should be find connecting the red wire directly to the battery. That wire is normally constant voltage at the fuse box anyway.

[smoken u]

well i have had issues in the past with the headlight circuit, i had to re-wire that as well, that was about 3 years ago lol, tommorrow when ive got some light to work with, ill run through the headlight circuit as well, then failing that, its gonna get the direct power. now the whole issue with not having the 12 volts form battery, im wondering if maybe a woire is corroded or chafed through under the battery tray where the harness loops under. hmmmmmmmmm lol looks like ive got myself quite the adventure for tommorrow morning